First report of powdery mildew caused by Erysiphe lonicerae var. lonicerae on Lonicera sempervirens in Korea

Trumpet honeysuckle (Lonicera sempervirens) is an exotic ornamental vine, which was recently introduced and widely planted in gardens throughout Korea. In September 2006, during a survey of diseases of ornamental trees and shrubs, severe outbreaks of powdery mildew on this plant were noticed in two parts of Seoul. White superficial mycelia and conidia were present epiphyllously on both sides of the leaves as well as on young shoots, forming thin, irregular colonies (Fig. 1). Infections often cause leaf distortions, withering and reduced growth.

The hyphae were septate, branched and 4-6 µm in width. Conidiophores were unbranched, cylindrical, 50-95 µm and composed of 3-4 cells. Conidia produced singly, were ellipsoid or doliiform, 28-37(-42) x 18-22 µm, without distinct fibrosin bodies. Chasmothecia were dark brown, spherical, and scattered subgregariously, 86-120 µm diameter. Each chasmothecium contained 5-10 asci (Fig. 2). Appendages arose equatorially, 6-14 per chasmothecium, and were 1.5-3.5 times as long as the chasmothecial diameter. They were substraight to somewhat flexuous, 6-9 µm in width, thick-walled at the base, gradually becoming narrower, aseptate or occasionally 1-septate. They were compactly and irregularly branched 3-5 times at the apex. Primary branches were often elongated. Asci were shortly stalked, 3-6-spored, 50-68 x 30-40 µm (Fig. 2). Ascospores were ellipsoid-ovoid, 21-28 x 10-13.5 µm. Based on these characteristics, this fungus was identified as Erysiphe lonicerae var. lonicerae (Braun, 1987, 1995).

Six species of Erysiphe are known to infect Lonicera spp. (Braun, 1987; Tanda, 2000): E. lonicerae (var. lonicerae and ehrenbergii), E. magnusii, E. erlangshensis, E. caprifoliacearum (var. caprifoliacearum and flexuosa), E. miurae and E. lonicerae-ramosissimae. These can be differentiated based on the length and septation of the chasmothecial appendages. Six native species of Lonicera are known to be associated with E. erlangshensis in Korea (Shin, 2000). The morphological patterns of the powdery mildew fungus on the exotic L. sempervirens, however, correspond to those of E. lonicerae var. lonicerae. Previously, this species was recorded on the trumpet honeysuckle from the USA and Estonia (Braun, 1995). This is the first report of the occurrence of powdery mildew on L. sempervirens in Asia. The voucher specimens are kept at Korea University (SMK 22270, 22300).